Musnad Ahmad 478:7

Ya'qub narrated to us, he said: My father narrated to us, from Ibn Shihab, from Ja'far ibn 'Amr ibn Umayyah, from his father, who said: "I saw the Messenger of Allah (peace and blessings of Allah be upon him) eating, cutting from the shoulder of a sheep. Then he was called to prayer, so he prayed and did not perform ablution."